Sound-record.



T. A. EDISON.

SOUND RECORD.

4. APPLIOATIGN FILED JAN. 3, 1907. 964,221 f Patented' July 12, 1910.

3 SHEETS-SHEET 1.

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T. A. EDISON.

SOUND RECORD.

APPLICATION FILED JAN. 3, 1907.

964,23 Patented Ju1y12,191o.

3 SHEETS-SHEET 2. 5

THE Nome/s PE'rsRs cal, wAsHmarnN, n. c.

.T. A. EDISON.

SOUND RECORD.

APPLICATION FILED JAN. 3, 1907.

945ml, v Patented Ju1y12,191o.

3 SHEETS-SHEET 3.

J9 Jy TH: Naam: PETERS cu., wAsHmcroN, n. c.

UNITE STAES PATENT EEIQE.

THOMAS A. EDISON, OF ORANGE, NEV JERSEY, ASSIGNOR TO NEW JERSEY PATENTCOMPANY, OF WEST ORANGE, NEW JERSEY, A CORPORATION OF NEW JERSEY.

SOUND-RECORD.

Specification of Letters Patent.

Patented July 12, 1910.

Application led January 3, 1907. Serial N o. 350,646.

To @ZZ whom it may concern:

Be it known that I, THOMAS ALvA EDISON, a citizen of the United States,residing at Llewellyn Park, Orange, county of Essex, and State of NewJersey, have invented certain new and useful Improvements inSound-Records, of which the following is a description.

My invention relates to various improvements in sound records, and myobject is to provide a. sound record of superior quality and sorelatively condensed that a much more extended reproduction may besecured from a cylinder of standard dimensions than is now possible.

As phonograph records are made under existing conditions, acircularedged recorder having a diameter of about .040 inch is engaged with arotating blank, so as to track very slightly below the surface, thesurface speed of the blank being upward of ninety feet per minute andthe available recording space being only one-hundredth of an inch inwidth. The diaphragm being caused to` vibrate under the effect of soundwaves, the recording stylus will partake of the same movements so as tothereby form the record, which will obviously consist of an enormousnumber of minute depressions or gouges, con nected together, and varyingin form and dimensions. Owing to the small available width of space inwhich the record may be formed, and to the fact that the recordingstylus is about four times as wide as that space, the deepestdepressions which can be formed without overlapping upon the adjoiningspaces, are extremely shallow, being about six ten-thousandths of aninch in depth. The walls of such a record groove in which the relationof width to depth is about sixteen to one, are of such slight curvaturethat difliculty is experienced in tracking the record, unless thereproducer stylus is mounted with great flexibility. Furthermore, withrecords of standard length, slightly over four inches, and turning atthe usual speed of 160 revolutions per minute, the available time inwhich to record the desired sounds is less than three minutes, so thatmany songs vor musical selections cannot be entirely recorded. It wouldbe inexpedient to reduce the surface speed of the blank, becauseexperience has shown that for the correct recording and reproduction ofmusic any attempt to materially reduce the relation oflength to width ofthe recorded waves or depressions, depreciates the quality of thereproduced sounds. In my Reissue Patent No. 11,857 of September 25th,1900, I discussed this point in detail. On the other hand, to make anychange in the dimensions of the records themselves, would unfit them foruse with hundreds of thousands of talking machines now on the market.Finally, under existing conditions times as wide as the space in whichit cuts, the resistance to the entrance of the cutting edge into thematerial, increases very rapidly for each succeeding increment of depth;or in other words, the energy required to force the cutting edge intothe material for the first quarter of the maximum cut is very much lessthan that required to force the cutting edge into the material for thefinal quarter of the maximmn cut. Consequently, sounds which arerelatively weak, are more perfectly recorded than very loud sounds,because with the former the amplitude of vibration ofthe recordingstylus will more nearly coincide with that of the sound waves.

WV hat I propose by my present invention is to produce a sound recordhaving the following characteristics: (l) It is of the standarddimensions of length and diameter, so that it may be used on existingtalking machines by making very slight changes therein. (2) The qualityof the recorded and reproduced sounds will be superior to that ofrecords made under existing conditions, without, however, in any wayaffecting the loudness of the reproduction, aud

the time of reproduction and of recording will be greatly extended,whereby songs and musical compositions now impossible of successfulrecording, may be satisfactorily recorded and reproduced. To securethese results, I make my improved l'ecord on a recording machine havinga feed screw with a much finer pitch than the present stand ard, andpreferably a pitch of two hundred threads per inch, and I make use of arecording stylus, the curve of which presents a circle whose diameter isonly about twice that of the available space, instead of four times thesame, as under existing conditions.

I find, as a result of calculation and experiand dealing with arecording stylus four ment, that. in order to cut a record to thepresent maximum depth in a space one-twohundredth of an inch wide,instead of oneone-hundredth inch, the recording stylus instead of beingone-half the diameter as that used in the latter case, as might besupposed, should in fact be only about onefourth the diameter, oraccording to my calculations, about .0105 inch. By making use of'a pitchof two hundred threads per inch, I obtain twice the length of recordgroove, so that if the surface speed remains unchanged, I am in this wayenabled to double the time of recording and reproducing. The change,however, would make it possible to materially reduce the surface speed,since owing to the narrowness of the record groove, a reduction in speedto half that now used, would result in the same relative shape of thewaves or depressions, and hence the latter could be tracked with thesame facility as those now made under existing conditions at double thespeed, if the reproducer stylus bore the same relation to the size ofthe record as at present. Since, however, the reprodueer stylus wouldhave a diameter of less than ten one-thousandths of an inch as againstthirty-five one-thousandths, it would track such a record with greaterfacility than can the present reproducers track the record groove as nowmade. Of course, to reduce the diameter of the reproducing stylus toone-fourth that now employed, and to reduce the surface speed one-half,would be to impose very much greater wear on the record surface, andwould necessitate the employment of very hard materials. With materialsof a waxlike nature adapted to be molded by casting, as II shallpresently describe, it will` production, since by making the width of'the record groove only one-half its present dimension without increasingthe length of the various depressions which characterize the same, andby reducing the diameter of the stylus to one-fourth the size now used,I am enabled to accurately track the extremely fine and delicateportions of the record representation of overtones and the finershadings of the principal tones. In other words, the effect issubstantially the same as if under existing conditions the surface speedwere doubled and the diameter of the reproducer ball were reducedone-half, without, however, encountering any foreign sounds that mightbe produced by such a high speed.

By employing a recording stylus, whose diameter is only about twice theavailable space in which to record, instead of four times the space asis now the case, the record groove will be formed with much more clearlydefined side walls, and consequently, the reproducer stylus will tracksuch a groove with greater ease and certainty than the very shallowgrooves that are formed under existing conditions. Furthermore, arecording stylus as I propose herein, more nearly approaches thetheoretically perfect device in which the resistance to the cuttingeffect is the same for each successive unit of,

the recording material to the same depth.`

By reason of this fact, with my improved.` arrangement, the recordgroove will be more nearly a graphic representation of the sound waves,and there will be less aberration in the reproduction, particularly onloud notes, than is now the case. Furthermore, by reason of the smalldiameter of such a recorder, it cuts more readily into the material andhence imposes a smaller resistance to the vibration of the diaphragmthan a` larger stylus, such as those now used. Consequently, thediaphragm may be made lighter and more responsive to the sounds. Inorder that the invention may be better understood, attention is directedto the accompanying drawings, forming part of this specification, and inwhich- Figure l, is a diagrammatic view, one hundred times enlarged,showing a recordrng stylus, as at present used, and illustrating therelative depth and width of its maximum cut; Fig. 2, a similar view,showing the improved recorder on the same scale; Fig. 3, a plan view onthe same scale, showing part of a record groove, formed by the recorderof Fig. l; Fig. 4, a similar view on the same scale, showing the samerecord formed by the recorder of F 2, at the same surface speed; Fig. 5,a similar' view `on the same scale, showing the same record formed bythe recorder of Fig. 2, at onehalf the surface speed; Fig. 6, adiagram-- matic sectional view, six hundred times enlarged showinggraphically the area of the material removed by the stylus of Fig. 1, incutting to the full maximum depth and to one fourth, one half, and threefourths thereof respectively; Fig. 7, a similar view on the same scalein connection with the stylus shown in Fig. 2; Fig. 8, a diagramillustrating graphically the area of material removed by the two formsof stylus, in the four positions shown in Figs. 6 and 7 Fig. 9, aperspective view of a suitable recording stylus for making improvedsound records, and Figs. l0 and l1, side and end views of a suitablereproducing stylus for engaging the same.

Similar parts are represented by the same reference numerals.

Referring rst to Fig. l, I show the recording stylus l, of a diameter of.O4 inch and tracking to the maximum depth in the recording material 2.rlhe depth of this cut is extremely slight, being in fact, only aboutsix ten-thousandths of an inch. Such a record groove is also veryshallow, its maximum width being about sixteen times its maximum depth,so that its side walls are hardly defined at all, and, in consequence,very slight side stresses will throw the reproducer out of the groove,to produce skipping In Fig. 3, I show a plan view of a part of a soundrecord, which would be formed by the recorder described. Many of thedepressions or waves are of greater length than width and hence can betracked by a spherical stylus, or more perfectly by a button shapedstylus as described in my reissue patent, but certain of thedepressions, which are frequently encountered in practice, and whichprobably are reperesentations of overtones or very weak fundamentaltones, are materially shorter than their width and are difficult toreproduce, except with a stylus having an objectionably narrow beadededge. It will be seen from Fig. 6, showing the same groove, in crosssection, many times enlarged, that the recorder in entering the materialfor the first quarter of its maximum movement is required to removeinuch less material than in movement during the next quarter, wherebythe resist-- ance offered to the stylus will very greatly increase as itcuts into the material. I have made a careful computation of the areasincluded within t-he dividing lines of this gure, and have plotted themon Fig. 8. Thus the line 5 6 may be considered as representing the areaof cross section of the material removed during the first quarter of thecut, or the resistance to the cutting tool; to the same scale, 7 8represents the area removed or resistance to cutting during the secondquarter, 9 1() during the third quarter and 11-12, the fourth quarter.The rate of increase of resistance to the cutting effect of the style,may be graphically represented by the curved line l, 5, 7, 9, 11. Fromthis diagram. it will be evident that as the stylus cuts into thematerial, the resistance encountered increases very rapidly, and becomesvery pronounced as the stylus reaches the maximum depth. Consequently,the record will be distorted, the portions thereof representing loudsounds being proportionately more imperfect than the portionsrepresenting weaker sounds.

Referring now to Fig. 2, I illustrate the new recording stylus 13, whosecutting edge presents a curve slightly more in diameter than twice thewidth of the available recording path, which I prefer to make onetwohundredths of an inch or thereabout. I find that in the case of twohundred threads per inch, the diameter of the stylus should be almostexactly .0105 inch to cut to the same depth as the stylus l in the caseof one hundred threads per inch. Such a record, as shown in Figs. 2 and7 is provided with very clearly defined side walls, its maximum widthbeing only about eight times its maximum depth, and in consequence thereproducer stylus will be kept in engagement therewith with much greatercertainty than in the case of the very shallow record groove of Fig. l.

In Fig. 4t, I illustrate the appearance of the same record shown in Fig.3, assuming it to have been made with the small recorder of Fig. 2, andat the same surface speed. Here it will be seen that the narrowing ofthe record groove has altered the shape of the depressions or waves, sothat the latter are apparently much extended (see for example, the twodepressions 3, 3) and the reproducer stylus can more readily engage andtrack the same, particularly since the diameter of the stylus is onlyabout one-fourth of that now used. In fact, to produce the same relativeformation of the waves or depressions, to give the effect shown in Fig.5, the surface speed would have to be reduced one-half. With very hardmaterial, that might be done with excellent results` but with wax-likematerials although relatively hard, I prefer to maintain the surfacespeed as-.at present, in order not to make the wear on the recordexcessive. At the same time, as already indicated, by maintaining thepresent surface speed so as to double the relative length to breadth ofthe individual depressions constituting the record, and by reducing thediameter of the rcproducer ball to about one-fourth, conditions arepresent under which the stylus will very much more perfectly track allportions of the record. In fact, those portions of the record whichunder existing conditions are not tracked at all, for instance, thoserepresenting the overtones of the finer shadings of the fundamentaltones, will be perfectly tracked under the conditions presented hereinso as to add materially to the quality of the reproduction.

In Fig. 7, I illustrate in cross section, many times enlarged. therecord groove made with the stylus of Fig. 2, and in which the samecomparison is made as in Fig. 6. Here it Will be seen, that the amountof material to be removed is not only much less than with the largerstylus, but the resistance to the cutting effect as the stylus entersthe material is more nearly uniform. This is perhaps better shown inFig. 8, where the area 4, 14, 6, represents the area of material removedby the stylus during the first quarter of its maximum cut; the area 6,14, 15, 8, the area for the second quarter; the area 8, 15, 16, 10 thearea for the third quarter; the area 10, 16, 17, 12, the area for thelast quarter. The rate of increase of resistance to the cutting effectof the style may be graphically represented by the curved line 4, 14,15, 1G, 17. A comparison of that line With the line 4, 5, 7 9, 11, showsvery graphically the diminished rate of increase of resistance to thecutting effect, in the case of the stylus of Fig. 2, as compared to Fig.1, and at the same time a comparison of the total areas of materialremoved at any given depth of cut by the respective recording styluses,discloses graphically the great difference in the work to be performedthereby, and the relative ease with which the smaller stylus enters thematerial. Of course, in making these comparisons between the two formsof stylus, I have not gone to the extent of determining the cubicalcontents of the masses of material removed by them but the comparison issufliciently illustrated by referring to cross-sectional areas alone.

From the comparison above made, it will be evident that with a recordingstylus, such as shown in Fig. 2, the distortion, due to the resistanceof the material to the cutting effeet will be considerably less thanwith the stylus shown in Fig. 1, and there will also be less differencein the distortion of records, representing loud sounds, and thoserepresenting weaker sounds, than is now the case, so that records madewith the improved stylus will be of superior quality than those whichcan be made under existing conditions. Furthermore, the stylus shown inFig. 2, cuts more readily than the stylus shown in F ig. l;consequently, the diaphragm with which it is used may be made moresensitive and therefore more readily responsive to the sound vibrations.

A form of recording stylus, suitable for cutting the extremely minuterecord, herein contemplated, is shown in Fig. 9, and is described indetail and claimed in an application filed by me on even date herewith.l/Vith this recording stylus the stylus is provided with a shank 18,formed with a button head 19, having a cutaway port-ion 20, so as toresult in the production of a cutting edge 21. The curve of the head 19is of a proper radius to give the desired maximum cut Within thenecessary restricted path offered for the reception of the record. In

the case of a ,record that is 200 threads per inch, the diameter of thecircle representing the cutting edge should be slightly greater than oneone-hundredth of an inch as I have previously explained. It will, ofcourse, be understood, however, that While such a recorder is entirelysuited for the purpose, any other form of stylus having a circular orapproximately circular cutting edge that is sufficiently small indiameter may be made use of.

In Figs. 10 and 11, I illustrate a suitable form of reproducing stylusfor engaging the very fine record, and which may be made of the desiredsmallness in diameter. This stylus comprises a cylindrical shank 22, thelower end of which is formed with a rounded engaging edge 23 toaccurately track the record, the stylus being preferably maintained inengagement with the record at substantially the angle shown. Like therecorder of Fig. 9, the reproducer shown in Figs. 10 and 11, may bereplaced by other forms of stylus, suitable for t-he purpose. In makingthe improved records, it is, of course, necessary to make use of arecording machine, the pitch of Whose feed screw is sufliciently finefor the purpose, say-200 threads per inch. Having obtained asatisfactory master in such a machine, I prefer to make duplicatestherefrom by any suitable process, instead of using them for directreproduction, since, owing to the fineness of the record groove, it isimportant that relatively hard material should be used, on which therecords could not be satisfactor-ily made in the first instance. Asuitable duplicating process by means of which copies may be made from amold secured from such a master, is disclosed in a patent of J. lV.Aylsworth, No. 855,605 granted J une 4, 1907, wherein the mold isrotated at a high speed and the molten material is caused to bedistributed over the bore thereof by reason of the centrifugal forcedeveloped, after which the rotation is continued until the material hasset sufficiently to maintain its shape. The material is then allowed tocool until it shrinks from the m-ld, after which the record is finishedon its interior, and ends, if necessary. If the records are to be madeof a wax-like material, as becomes readily possible with such a processas that indicated, I select a material which is very hard and tough, soas to resist the wear, which would be obviously greater than if a largerstylus is used, as under present conditions. Suitable materials may,however, be made, which will be sufliciently tough as to permit theimproved records to compare favorably as to their wearing qualities withrecords made under existing conditions. An example 'of such acomposition is disclosed in an application of J. W. Aylsworth, filedNovember 7 1906, Serial No. 342,318, said composition comprising amixture of asphalt, stearate of lead and a resin gum. In using myimproved records on existing talking machines, the only changes thereinwhich will be required will be the substitution of a finer reproducingstylus, possibly a more sensitive diaphragm, and mechanical connectionsby which the stylus will be caused to track the ner thread of therecord. This latter may be done by either substituting a finerpitch feedscrew on the reproducing machine, or by making use of a differentialfeed mechanism, or any desired connections between the driving shaft andthe feed screw, by which the desired feed of the reproducer arm may beeffected from the original 100 thread feed screw of the presentstandard.

It will be understood that where in the claims I refer to my soundrecord as one whose record groove is approximately circular in crosssection, the latter may be a curve which is either circular or closelyapproximates the arc of a circle within the limits of the record groove.Thus, the groove is circular if cut by the recorder shown in Fig. 9, orby the recorder shown in Fig. 2 if the shank thereof is maintainedparallel to the record surface. If, however, the shank of the recorderstylus is set at an acute angle to the record surface, as for example,an angle of l0 to 20 degrees, as is usual in practice, the cross sectionof the groove will be an arc of an ellipse of such slight eccentricity,however, as to very closely approximate the arc of a circle. Similarlyif the recorder has a cutting edge which only approximates a circle, thegroove cut thereby would accordingly vary slightly from the circular incross section.

Having now described my invention, what I claim as new and desire tosecure by Letters Patent is as follows:

l. As a new article of manufacture, a duplicate sound record made of ahard tough material, whose record groove is substantially circular incross section, of a pitch of approximately 200 threads per inch, and themaximum depth of which groove is greater than l of its maximum width,substantially as set forth.

2. As a new article of manufacture, a duplicate sound record made of ahard tough material, whose record groove is substantially circular incross section, has approximately 200 threads per inch, and is of amaximum depth approximately one-eighth of its maximum width,substantially as and for the purposes set forth.

3. As a new article of manufacture, a sound record having a continuousrecord groove formed thereon having a pitch of approximately 200 threadsper inch, the record groove having in cross section approxi- -mately theform of an arc of a circle the diameter of which is approximately twicethe maximum width of the groove, substantially as set forth.

4. As a new article of manufacture, a sound record having a continuousrecord groove formed thereon having a pitch materially finer than `100threads per inch, the record groove having in cross sectionapproximately the form of an arc of a circle the diameter of which isless than .013 inch, the maximum depth of the groove being greater thanits maximum width, and the gouges or waves of maximum width occupyingsubstantially all the available space transversely of the record groove,substantially as set forth.

5. As a new article of manufacture, a sound record having a continuousrecord groove of the vertically-undulating type formed thereon having apitch materially finer than 100 threads per inch, the record groovehaving in cross-section approximately the form of an are of a circle thediameter of which is between three times and one and one-half times themaximum width of the groove, the maximum depth of the groove beinggreater than 6 its maximum width, substantially as set forth.

This specification signed and witnessed this 28th day of December 1906.4

THOS. A. EDISON. lVitnesses:

FRANK L. DYnR, ANNA R. KLEHM.

